The use of Anger-type scintigraphic cameras has become widespread in Nuclear Medicine practice. Their high sensitivity and ease of operation provide a sound basis for their popularity. However, the scintillation camera can drift from optimum performance in four major ways: loss of sensitivity, increase in non-uniformity and non-linearity and loss of spatial resolution. It has been suggested that these effects not only mask certain real abnormalities but also contribute to false positive readings by the physician. A series of studies to quantitatively evaluate the effect of these parameters on the detectability of lesions in computer-simulated scinti-grams is suggested. The investigation proposes to systematically degrade sensitivity, uniformity, linearity and resolution from the basic (in scatter) three-dimensional response of a typical Anger camera. The range of degraded responses will be limited to that which might be expected in slightly malfunctioning clinical units. Using an established digital computer system, liver images containing cold spherical voids will be generated to simulate those expected clinically under similar degraded conditions. The effects of these degradations will be measured by quantifying observers' responses to the resultant images. If this study shows that there are significant differences in detectability with even slight deviations from optimum camera operation, these data could help provide a basis for a more concentrated effort in daily quality assurance testing.